I like Earth Light, Power Within The Land and Underworld Initiation by R J Stewart.

Demonology, A Field Guide to Demons, fairies, fallen angels and other subversive spirits by Carol K. Mack and Dinah Mack. This one is interesting and can be accessible and well organized. The demons, fairies and other mythical beings featured in this book were taken from the legends and folklore of several cultures and they are grouped according to their place of residence: water, mountain, forest, desert, domicile and psyche. Each chapter includes a short description of the creature's appearance, habits and preferences; one of two stories of encounters with it; and a section on disarming and dispelling techniques. But its more of a history lesson on the very basic entities out there, not a true "guide" it covers the "best" known, but does not venture into the beings that are older and possibly, more "subversive".

You guys can all read about the "72 Goetic Demons" online fairly easily (google is magick, lol), if this is a subject that interests you. These demons are supposedly the ones that King Solomon locked away.